Thousands of tables versus on table?

I have several thousand clients. Our clients do surveys, and each survey
has two tables for the client data,

responders
responses

Frequent inserts into both table.

Right now, we are seeing significant time during inserts to these two
tables.

Some of the indices in tableA and tableB do not index on the client ID
first.

So, we are considering two possible solutions.

(1) Create separate responders and responses tables for each client.

(2) Make sure all indices on responders and responses start with the
client id (excepting, possibly, the primary keys for these fields) and
have all normal operation queries always include an id_client.

Right now, for example, given a responder and a survey question, we do a
query in responses by the id_responder and id_survey. This gives us a
unique record, but I'm wondering if maintaining the index on
(id_responder,id_survey) is more costly on inserts than maintaining the
index (id_client,id_responder,id_survey) given that we also have other
indices on (id_client,...).

Option (1) makes me very nervous. I don't like the idea of the same sorts
of data being stored in lots of different tables, in part for long-term
maintenance reasons. We don't really need cross-client reporting, however.

=thomas